A method of manufacturing a seal for roller bearing, seal for a roller bearing and a roller bearing provided with such a seal

Abstract: The invention relates to a method of manufacturing a seal for a roller bearing, for instance a ball bearing. The seal according to the invention is formed from a thermoplastic polymer-containing material which is subsequently cross-linked under the influence of radiation, for example β-radiation. This allows the use of seals manufactured according to the invention at near or even above the melting point of the non-cross-linked thermoplastic polymer being employed. Due to the invention a large number of cheap polymeric materials have become suitable for the manufacture of seals, and due to the cross-linking the swelling caused by lubricants can be reduced considerably.

Description: The present invention relates to a method of manufacturing a seal having a first part and a second, sealing part whereby a seal is formed from a thermoplastic polymer-containing material, said material subsequently being cross-linked under the influence of radiation, the irradiation of the first and second parts being different. Such a method is known from DE 2.654.931. This publication describes a method of cross-linking elastomeric compounds for seals for pneumatic or hydraulic purposes as well as seals for shafts. The object is to provide seals with reduced coefficient of friction while several other properties such as hardness can be modified as well. The present invention aims to provide a method of manufacturing polymer-containing seals for rolling element bearings. To this end the method according to the invention is characterized in that the seal is a seal for a rolling element bearing, the first part is cross-linked to a degree that it provides a form-retaining part, and the second part is cross-linked to a degree that it provides a sealing, elastic part. As a result a seal can be manufactured in a simple and effective manner, formed from thermoplastic polymer-containing materials, whereby cross-linking under the influence of radiation adapts the properties of the material such that the seal is better suited for use near or above the melting point of the thermoplastic polymer. A seal formed from thermoplastic polymer-containing material cross-linked by radiation will during use in a rolling element bearing near or above the melting point of the original thermoplastic polymer retain its form and will only show mechanical wear. A preferred embodiment of the method uses ionizing radiation and in particular β-radiation. This is an effective manner to bring about cross-linking of the polymer material. Cross-linking the various parts of the pre-formed seal to a different degree can be advantageously carried out by adapting the radiation intensity and/or duration. By cross-linking the different parts of the pre-formed seal to a different degree their properties, such as rigidity, are adapted to the function of the particular part. When manufacturing a seal having a sealing, elastic part and a form-retaining part, cross-linking thus promotes good adherence between the respective parts. It is possible to manufacture the seal by means of injection moulding. This allows the seals according to the invention to be manufactured economically. In an advantageous embodiment the method is characterized in that injection moulding is carried out in one single step. Seals according to the invention can be manufactured by injection moulding in one single step achieving very good bonding between a sealing, elastic part and a form-retaining part of the seal. One preferred embodiment of the method according to the invention is characterized in that the same polymer-containing material is used for a seal having a sealing, elastic part and a form-retaining part. This contributes to an optimal bond between the sealing, elastic and the form-retaining part of the seal. According to another very advantageous embodiment the form-retaining part constitutes at the same time a cage or cage part. Such an embodiment contributes to the simpler assembly of a rolling element bearing formed with the seal. Moreover, because of less wear the operational life is longer and the sealing better. Another embodiment of the method is characterized in that additives, in particular fibres are incorporated in the polymer-containing material. By using additives the properties of the seals, in particular their different parts, are adapted to the functional demands of those different parts. The fibres can advantageously be glass fibre or carbon fibre. This allows especially the form-retaining part of the seal to be reinforced. Another embodiment is characterized in that the additive is a plasticizer and/or an elastomeric material. This makes it possible to confer especially on the sealing elastomeric part of the seal the desired elastomeric properties. Such additives can also promote cross-linking when using polymers that cross-link with difficulty,. The invention will now be elucidated with the aid of the drawing showing examples of embodiments of the invention. Fig. 1 is a very schematic view from above of a seal for a rolling element bearing. Fig. 2 is a cross section along the lines II-II as shown in Fig. 1 of a seal for a rolling element bearing according to the prior art. Fig. 3 is a schematic illustration of a step in the manufacturing process of a seal. Fig. 4 is a cross-section corresponding to Fig. 2 of a seal according to the invention. Fig. 5 and Fig. 6 represent, in a similar way as Fig. 2, embodiments of seals according to the invention. Fig. 7 represents an axial cross section of a rolling element bearing according to the invention. Fig. 1 shows a seal for a rolling element bearing in which the reference number 1 indicates a sealing elastic part which prevents lubricant from being released from the rolling element bearing. The seal further comprises a form-retaining part 2. The rigidity of the form-retaining part 2 allows the elastic part 1 to effectively carry out its sealing function. In the cross section of a seal according to the prior art as shown in Fig. 2, the elastic part 1 is an elastomer and the form-retaining part 2 is an inserted metal piece. A disadvantage when using thermoplastic elastomers is hereby the poor bonding between the two parts. Also, as the seal consists of two parts, its manufacture is rendered more difficult. According to the invention a seal for a rolling element bearing is manufactured by cross-linking a thermoplastic polymer-containing material by radiation. Examples of such thermoplastic elastomers are polypropylene, polyethylene, etc., these polymers are also cheap. They are cross-linked to various degrees, depending on the function of the different seal parts for a rolling element bearing. A greater degree of cross-linking means greater rigidity. In order to cross-link different seal parts to different degrees the radiation intensity can be adjusted. This is indicated in Fig. 3 with arrows, whereby the intensity I 0 is lower than I 1 . Instead of adjusting the radiation intensity, the duration of radiation for the parts having a sealing function can be shortened in relation to the duration of radiation for the form-retaining parts. Naturally, a combination of adjusting the radiation intensity and the length of radiation time also belongs to the possibilities. The elastic character of the polymer-containing material, possibly provided with plasticizer or elastomer, will be retained at least to some degree, while the form-retaining part 2 is more rigid than the sealing, elastic part 1, because of a higher degree of cross-linking. In this manner the seal according to the invention as shown in Fig. 4 is formed. When injection moulding the seal, whereby the sealing part 1 and the form-retaining part 2 are formed in separate steps, and in the case that said parts consist of different materials, the sealing elastic part 1 is strongly bonded with the form-retaining part 2. The properties of the material can be further adapted by using additives such as fibre. This can increase the rigidity of the form-retaining part 2 as well as the bond between parts 1 and 2. The fibre can, among others, be glass fibre or carbon fibre. If the polymer used crosslinks with difficulty, as is the case with polyamide, then the use of cross-linkable additives is desirable. Examples of such additives are cross-linkable polymers, such as for instance polyethylene. The embodiments of the seal for a rolling element bearing shown in Fig. 5 relate to a seal which is especially suitable for use when the sealing part is in axial contact with the inner race ring of the rolling element bearing rotating in relation to the seal, while the variant shown in Fig. 6 is a seal according to the invention for use when the sealing part is in radial contact with said inner ring. In a preferred embodiment the invention also relates to the manufacture of a seal whereby the form-retaining part constitutes a cage or cage part or is formed thereon. To avoid damage, for instance microcracks, of the cage or the cage part, the cage or cage part is built into the rolling element bearing before cross-linking. Fig. 7 shows an axial cross section of part of a rolling element bearing. the form-retaining part 2 of the seal shown here is provided with cage parts 3 in which balls 4 are incorporated. In the embodiment represented here the sealing, elastic parts seal on to the smooth sides of the inner race ring 5 and outer race ring 6 respectively. In such an embodiment the sealing, elastic parts are less liable to wear because of a relative lower velocity in respect to the inner and outer race ring. At the same time the manufacture of such a rolling element bearing is simple and cheap, because there is no necessity for special grooves and notches. Naturally the side shown in Fig. 7 without a seal can also be provided with a seal that is or is not connected to the cage parts.

Claims: A method of manufacturing a seal having a first part and a second, sealing part whereby a seal is formed from a thermoplastic polymer-containing material, said material subsequently being cross-linked under the influence of radiation, the irradiation of the first and second parts being different, characterized in that the seal is a seal for a rolling element bearing , the first part is cross-linked to a degree that it provides a form-retaining part, and the second part is cross-linked to a degree that it provides a sealing, elastic part. A method according to claim 1, characterized in that the radiation applied is ionizing radiation. A method according to claim 2, characterized in that the ionizing radiation applied is β-radiation. A method according to any one of the preceding claims, characterized in that the various parts of the pre-formed seal are cross-linked to different degrees by adapting the radiation intensity and/or duration. A method according to any one of the preceding claims, characterized in that the seal is manufactured by injection moulding. A method according to claim 5, characterized in that injection moulding is carried out in one single step. A method according to any one of the preceding claims, characterized in that the same polymer-containing material is used for the sealing, elastic part and the form-retaining part. A method according to claim 7, characterized in that the form-retaining part constitutes at the same time a cage or cage part. A method according to any one of the preceding claims, characterized in that in the polymer-containing material an additive is incorporated. A method according to claim 9, characterized in that the additive used is fibre. A method according to claim 10, characterized in that the fibre used is glass fibre or carbon fibre. A method according to claims 9 to 11, characterized in that the additive used is plasticizer and/or elastomeric material. A seal for a rolling element bearing, characterized in that the seal is manufactured according to the method of any one of claims 1 to 12. A rolling element bearing, characterized in that the rolling element bearing is provided with a seal according to claim 13. Use of a seal manufactured according to the method of any one of claims 1 to 12 for the manufacture of a rolling element bearing.

Inventors: BRAS JOHAN CHRISTIAN MARINUS, TADIC VENDRAN ANDELO, BRAS, JOHAN CHRISTIAN MARINUS, TADIC, VENDRAN ANDELO
Applicants: SKF IND TRADING & DEV, SKF INDUSTRIAL TRADING & DEVELOPMENT CO, B.V.
Application year: 1994
Main classification: F16C33
IPC codes: B29C35, B29C71, F16C33, C09K3